1.表经常发生的事情、存在的动作或状态 eg She sings with the band Crazy Boy. 2.表内心活动感情等 eg I don't think you are right. 3.描述客观真理 eg Birds fly in the sky. 4.表预定的行为 eg The train leaves at 9.
1.表过去发生的事情或存在的状态 eg Suddenly,the clouds cleared and the rain stopped. 2.表过去经常发生的事情 eg I was very thin in my childhood. 3.带有确定的过去的时间状语 eg Did you meet yesterday? He left just now.
1.要在将来的某个时间内发生，是“纯粹的将来动作”。 eg I shall / will not be free tomorrow. 2.表说话人的意图、打算或某种可能性 eg Who is going to speak first? 3.按计划要发生的动作或命令他人做某事 eg The new bridge is to open to traffic in 3 days.
1.说话、写文章的当刻正在发生的动作 eg They are having a football match. 2.现阶段一直在进行的动作 eg He is preparing for CET Band Six. 3.表示说话人的情感，如赞许、批评等 eg She is often doing well at school. 4.表示在近期按计划或安排要发生的动作 eg Are you staying here till next week?
1.表示在过去某时刻正在进行的动作 eg At this moment yesterday, I was packing for camp. 2.用于故事的开头，交代故事发生的背景情况 eg One night, he was typing in his study . Suddenly , a man broke … 3.表示在过去的未来时间要发生的动作 eg We left there when it's getting dark.
1.发生在“过去的过去” eg When I woke up, it had stopped raining. 2.与一个表示过去的时间状语连用 eg Peter had collected more than 300 Chinese stamps by the time he was ten. 3.在过去某时之前开始一直延续到这一时间 eg By the end of last year, he had worked in the factory for twenty years.
1.表示截止现在业已完成的动作 eg By now, I have collected all the data that I need. 2.表示发生在过去而对现在产生影响、带来结果的动作 eg She has been to the United States. 3.表示过去发生的动作持续到现在，并可能还要延续 eg I have learned English for 8 years.
1.宾语从句或间接引语中 eg He didn't expect that we would all be there. 2.表示过去习惯性的动作 eg During that period, he would do this every day. 3.表示过去的愿望、倾向，多用于否定句 eg They knew that we would never permit such a thing.
